Short Answer

Zwitterions are molecules that contain both positive and negative charges on different atoms but are electrically neutral overall.

A common example is amino acids, which have a positively charged amino group (–NH₃⁺) and a negatively charged carboxyl group (–COO⁻) in the same molecule. Zwitterions are important in biology, chemistry, and pharmaceuticals due to their unique chemical properties.

Detailed Explanation :

Definition of Zwitterions

A zwitterion is a chemical species that has separate positive and negative charges on different atoms within the same molecule, but the net charge of the molecule is zero.

• The term “zwitterion” comes from the German word “Zwitter”, meaning hybrid or double-being.
• Zwitterions are internal salts, formed when proton transfer occurs within a molecule.

1. Formation of Zwitterions

• Zwitterions commonly form in amino acids under certain pH conditions.
• In water, an amino acid like glycine can exist as:

• Here:
  • Amino group (–NH₂) gains a proton → –NH₃⁺ (positive charge)
  • Carboxyl group (–COOH) loses a proton → –COO⁻ (negative charge)
• The molecule remains electrically neutral despite having two opposite charges.

2. Properties of Zwitterions

1. Electrical Neutrality
   • Although they contain charges, the overall charge is zero.
2. Solubility
   • Zwitterions are highly soluble in water due to their ionic nature.
   • They can form hydrogen bonds with water molecules.
3. High Melting Points
   • Zwitterions exist as crystalline solids at room temperature, often with high melting points.
4. Amphoteric Behavior
   • Zwitterions can act as acids and bases depending on the surrounding pH.

3. Examples of Zwitterions

1. Amino Acids
   • Glycine: H₃N⁺–CH₂–COO⁻
   • Alanine, serine, lysine also form zwitterions.
   • Present predominantly at isoelectric point (pI), where net charge = 0.
2. Peptides
   • Chains of amino acids contain zwitterionic groups at termini and side chains.
3. Other Molecules
   • Betaine: trimethylglycine, found in plants.
   • Phosphatidylcholine: a zwitterionic phospholipid in cell membranes.

4. Importance of Zwitterions

1. Biological Significance
   • Amino acids exist as zwitterions in physiological pH, essential for protein structure and enzyme activity.
   • Zwitterionic groups help maintain electrostatic interactions in proteins.
2. Buffering Capacity
   • Zwitterions can resist pH changes, acting as internal buffers in biological systems.
3. Industrial Applications
   • Zwitterionic detergents are used in pharmaceuticals, cosmetics, and cleaning products.
4. Electrochemical Behavior
   • Their ionic nature makes zwitterions important in electrophoresis and chromatography techniques.

5. Summary

• Zwitterions are molecules with both positive and negative charges on different atoms.
• Common examples: amino acids (glycine, alanine), peptides, betaine.
• Properties: electrically neutral, water-soluble, amphoteric, high melting point.
• Biological and industrial significance includes protein function, buffering capacity, and chemical applications.

Conclusion

Zwitterions are unique molecules that possess dual charges but remain electrically neutral. They are most commonly found in amino acids, which exist in zwitterionic form in aqueous solutions at physiological pH. Their chemical properties, solubility, and amphoteric nature make them vital for biological processes, protein structure, and industrial applications. Understanding zwitterions is essential in chemistry, biochemistry, and pharmaceutical sciences.